This invention relates to oil-in-water lubricant-coolant emulsions used in metalworking operations (hereinafter, "emulsion(s)") such as rolling, cutting cupping, drawing and ironing, milling, scalping, drilling, grinding, punching, and the like. In particular, it relates to a method for adding a fatty acid to such emulsions, thereby maintaining a preselected level of lubricity agent in the emulsion.
In methods of shaping metals in which lubrication is required, it has become common practice to use emulsions in place of prior used non-aqueous hydrocarbon lubricants. For example, in rolling a metal such as aluminum, magnesium, or steel through steel work rolls it is usual to use an emulsion to flood the tool and the workpiece. As used herein "tool" is used broadly to refer to any piece of equipment with which the metal is in contact during the metalworking operation, e.g., rolls, punches, dies, drills, cutting devices, grinding devices, and the like. The emulsion serves the dual function of both coolant and lubricant. As a coolant in cutting operations, the emulsion helps to control the temperature of the cutting tool. As a coolant in other shaping operations, for example, in rolling, the pattern of distribution of the emulsion on the work rolls is regulated to control the temperature gradient of the rolls transversely to the work stock and hence the shape of the rolls is controlled. The rate of flow of the emulsion onto the metal being shaped regulates the temperature thereof during the various stages of shaping.
As a lubricant, the emulsion serves: (1) to control the frictional forces existing between the workpiece and the tool; (2) to promote the development of desired tool coatings during the shaping process, e.g., rolled-coating during rolling; (3) to prevent excessive transfer of metal from the workpiece to the tool or from the tool to the workpiece, e.g., between the rolls and the workpiece as in rolling operation; and (4) to facilitate removal of the workpiece from the tool, e.g., as in punching operations.
Typical emulsions that have been used for metal shaping operations such as rolling or cutting have consisted essentially of from about 0.5 to 20% by weight of an oil in the water, the oil being a mixture referred to in the trade as a neat soluble oil or simply soluble oil. Such neat soluble oil is widely sold as a concentrate containing, generally, about 70-90 percent by weight of a base oil, such as a light mineral oil, from about 1 to about 20 percent by weight, based on said neat soluble oil, of one or more anionic and/or nonionic oil-in-water emulsifying agents and the balance substantially water. For most metal shaping operations, the neat soluble oil must contain from about 0.5 to about 15 percent by weight lubricity additives such as long chain alcohols, e.g., C.sub.12 to C.sub.16 alcohols, long chain fatty acids, e.g., C.sub.12 to C.sub.22 acids such as oleic acid, and salts or esters thereof, e.g., alkanolamine soaps, or, esters such as butyl stearates which serve as extreme pressure agents. Emulsions are made up conventionally by admixing one of the commercially available substantially water-free concentrates with water. The commercial concentrates usually contain up to 0.5 percent by weight of a bactericide and from about 0.5 to about 5 percent by weight of a coupling agent, i.e., a substance which stabilizes the concentrate during storage prior to use.
Since, as will become apparent, this invention employs an additive solution as a means for controlling the concentration of a lubricity additive, i.e., the active ingredient in the oil phase of the emulsion, to avoid confusion the phrase "lubricity agent (s)" is used hereinafter to refer to the active component usually referred to in the trade as "lubricity additive". "Fatty acid-type lubricity agent (s)" refers to long chain fatty acids and mixtures thereof, and may, but need not necessarily, include one or more alkali metal or ammonium salts thereof. "Free fatty acid(s)" refers to long chain fatty acids and mixtures thereof, substantially free from their corresponding alkali metal and ammonium soaps.
The composition of the neat soluble oil itself forms no part of the present invention. The method and composition of the invention are usable with substantially all of the commonly known and used, commercially available neat soluble oils, without modification of the soluble oil per se.
Representative commercial compounded oils, i.e., soluble oils, include, for example, Solvac 1535G, Prosol 44, Prosol 66, Prosol 172, and Mobil 200C, all supplied by Mobil Oil Company; Rollex A supplied by the Shell Chemical Company; RolKleen #53 supplied by the D. A. Stuart Oil Company, Limited; A-100 supplied by the Far Best; Tandemol C86 and Tandemol K87 supplied by E. F. Houghton and Company; Texaco 591 supplied by Texaco, Inc.; and Quakerol 538 supplied by the Quaker Chemical Corporation.
A typical neat soluble oil that is commercially available has the following general composition, by weight:
______________________________________ Components Percent ______________________________________ Light Mineral Oil 83 Lubricity Agents 11 Emulsifiers 4 Coupling Agents 0.5 Bactericide 0.5 Detergent 1 ______________________________________
The base oil used in making up a neat soluble oil generally is selected from a light hydrocarbon or light hydrocarbon mixture having a viscosity of about 40 to 200 Saybolt Universal Seconds (SUS) at 100.degree. F. However, other lubricious materials such as fatty oils, e.g., palm oil, or synthetic materials, e.g., palm oil substitutes are also used as a base oil making up soluble oil. Such other lubricity materials may have viscosities as high as about 850 SUS.
For the purposes of the following description and the appended claims, the term base oil is understood to encompass the light hydrocarbon or hydrocarbon mixtures recognized as light mineral oils, in addition to lubricious materials including vegetable oils, such as palm oil, animal fats such as lard oil, and palm oil substitutes and the equivalents thereof, e.g., polyglycols and ethers and esters thereof, silicones and polysilicones, carbonates, mercaptals, formals, and other synthetic lubricating oils known to the art, selected from those which are non-staining of the particular metal being shaped.
Suitable anionic oil-in-water emulsifiers used in sufficient amount to emulsify the base oil include, for example: (1) alkylarylsulfonates such as the higher alkylbenzene sulfonates wherein higher alkyl means an alkyl group having at least 8 carbon atoms, e.g., C.sub.12 H.sub.25 C.sub.6 H.sub.4 SO.sub.3 Na; (2) fatty alkyl sulfates such as CH.sub. 3 (CH.sub.2).sub. 10 OSO.sub.3 Na; (3) the sulfonated fatty amines such as C.sub.17 H.sub.33 CON(CH.sub.3 )C.sub.2 H.sub.4 SO.sub.3 Na; (4) the alkali metal salts of sulfonated fatty acids; and the like. The other alkali metal salts of these compounds and the triethanolamine salts are equivalents of the sodium salts described above. The alkanolamine soaps of long chain fatty acids are particularly suitable, e.g., diisopropanolamine, diethanolamine or monoethanolamine salts of oleic acid, palmitic acid or stearic acid, the salts being useful singly or as mixtures.
Suitable nonionic oil-in-water emulsifiers include the nonionic ethers such as those derived from alkylphenols and ethylene oxide, e.g., C.sub.8 H.sub.17 C.sub.6 H.sub.4 OC.sub.2 H.sub.4 (OC.sub.2 H.sub.4).sub.x OH wherein x has a value of 9 to 14 or more, the primary alcohol-ethylene oxide adducts, and the secondary alcohol-ethylene oxide adducts.
When one of the described emulsions is placed in service in metal shaping operations it tends to work well initially both as a coolant and as a lubricant; in fact, it is commonly observed that the metal surface obtained in metal shaping operations is improved after several days of using the emulsion. The effectiveness of emulsions as lubricants, however, has been observed to deteriorate thereafter. Use of filtration techniques combined with control of water hardness, such as taught in U.S. Pat. Nos. 3,408,843 and 3,409,551, greatly prolongs the life of an emulsion, and is certainly preferred even when using the present invention. Nevertheless, a decrease in the quality and capacity of production occurs where only filtration and control of hardness is used.
Some degree of success has been achieved in control of emulsions by monitoring and adjusting of pH, by adding base oils and/or emulsifiers to control the oil particle size, and the amount of free oil (i.e., non-emulsified) and emulsified oil in the system, and the like.
It has also been realized that control of the balance of the various lubricity agents (not to be confused with the base oil) in the oil phase is critical, and it is this aspect which is the subject of the present invention. As an emulsion is used, the lubricity agents are gradually depleted, for example, by carry out on the workpiece, by degradation by bacteria and heat, by reaction with metal fines and other contaminating substances, and the like. Moreover, particicularly where an emulsion is used wherein the emulsified oil phase comprises a relatively low percentage of the total emulsion, various oils entering the system, such as leaking gear lube oil, hydraulic oil, and the like, can act as diluents of the lubricity agents.
To further explain this latter point, for any given operation, it is known there is an optimum range of emulsified oil content in the emulsion. As oil is carried out on the workpiece, neat oil containing the lubricity agent can be added to the emulsion to restore both the oil level and the lubricity agent, assuming there is no oil leaking into the system. Where oil is leaking into the system, however, as is most always the case, the leaking oil usually does not contain the required lubricity agents. Moreover, while much of it separates as free oil, at least some of the leaking oil becomes emulsified in the system, by design or naturally. Particularly where an emulsion is employed where the emulsified oil content is designed to be relatively low, e.g., on the order of 2 to 12 weight percent of the emulsion, the net result is that the amount of newly emulsified oil entering the system through leakage represents a significant fraction of that lost through carryout. Consequently, little neat oil containing the lubricity agent can be added without upsetting the oil:water ratio, so that while the total amount of emulsified oil remains more or less constant or is depleted at a relatively slow rate, the lubricity agent is depleted at a much faster rate. Unless the proper balance of lubricity agents is restored, a host of problems arise, such as excessive tool wear, scratching of the surface of the workpiece, and in extreme cases, actual tearing or wrinkling of the workpiece, and the like.
Any substance which is added to the emulsion actually first contacts the continuous aqueous phase. The various lubricity agents, however, must be worked into the discontinuous oil phase, or at least onto the oil droplet surface, to be effective. Thus, it is not surprising that poor additive recovery is obtained where attempts have been made to add the additive directly to the emulsion. That others not practicing this invention are experiencing such difficulties has been illustrated recently in a paper by R. G. Tidwell, "Modern Hot Mill Emulsion Controls", presented in May, 1975, at the 1975 Annual Meeting of the American Society of Lubrication Engineers Non-Ferrous Metals Council wherein it was stated "A 50 percent recovery [i.e. effective incorporation into the oil phase of the emulsion] of most fatty additives will generally be a good recovery" . In the same paper Tidwell suggests a 75 percent recovery can be realized if the additives are added to neat oil and then made into an emulsion in a tank equipped with an agitator and a heat source. Nevertheless, the inability to easily add lubricity agents to the emulsion leads to waste of raw materials, premature disposal of emulsions, variations in product quality, loss of production, and generally inefficient operation.